[2] Because of these peculiar conditions, these thermae differed in plan from all others in the city – no anterooms were provided on either side of the caldarium, for instance, since the building was too narrow.

The frigidarium seems to have had its longer axis aligned north and south instead of east and west, and behind it were tepidarium and caldarium, both circular in shape.

They were restored in 443 by the city prefect Petronius Perpenna Magnus Quadratinus,[4] at which time it is probable that the colossal statues of the Dioscuri and horses, now in the Piazza del Quirinale, were set up within them.

[5] The Baths of Constantine probably remained in use until the Gothic War (535–554), when all but one of the aqueducts to the city of Rome were cut by the Ostrogoths.

Enough of the structure was standing at the beginning of the sixteenth century to permit plans and drawings by architects of that period; these are the chief sources of our knowledge of the building.